Chlorohydrocarbon and chlorofluorocarbon propellants used in medical aerosol formulations are generally considered to be environmentally unfriendly. Therefore, these propellants have been largely replaced by hydrofluoroalkanes such as 1,1,1,2 tetrafluoroethane ("HFA -134a") and 1,1,1,2,3,3,3 heptafluoropropane ("HFA-227ea") that have been identified as safe for use in pressurized metered dose inhalers.
Medicinal aerosol formulations are generally of the solution or suspension type. Each type is composed of at least the medicament and the propellant. The solution type aerosol formulation contains the medicament dissolved or solubilized in the propellant, or a mixture of propellant and cosolvent. The suspension type aerosol formulation contains the medicament in the form of particles which are dispersed in the propellant. The suspension type aerosol formulations usually contains a surfactant, and can also include a cosolvent. Conventional Budesonide aerosol formulations are of the suspension type. Conventional Formoterol aerosol formulations are of the solution and suspension type.
U.S. Pat. No. 5,736,124 (Akehurst) discloses a suspension type aerosol formulation in which the medicament is in the form of particles dispersed in a cosolvent. The cosolvent is present in an amount less than 5% by weight to avoid dissolving the medicament (column 4, lines 13-24).
Published International Application No. WO 98/05302 discloses a suspension type aerosol formulation in which the medicament is in the form of particles dispersed in a cosolvent. The cosolvent can be present in amount of from 6 to 25% by weight. However, this application teaches that the medicament and cosolvent selected should be such that the medicament is not dissolved in the cosolvent and the particulate shape of the medicament is retained.
Ethanol has been used as a cosolvent. However, previous teachings such as European Patent No. EP 0 616525 have taught away from using concentrations of ethanol greater than 5% in solution aerosol formulations for .beta.-agonists.
Each of the drugs Budesonide and Formoterol has proven difficult to formulate into conventional aerosol compositions. Such formulations have exhibited short shelf-lives and require refrigeration. Refrigeration is undesirable because many patients are required to carry the aerosol canisters on their persons. There remains, therefore, an important need for aerosol formulations containing Budesonide and Formoterol that remain chemically and physically stable during storage at ambient conditions of temperature and humidity.